html,
body {
    height: 100%;
    width: 100%;
    margin: 0;
    padding: 0;
    overflow: hidden;
    background: #000;
    text-align: center;
}

body:before {
    content: "";
    display: inline-block;
    height: 100%;
    vertical-align: middle;
}

.g-container {
    display: inline-block;
    perspective: 4px;
    perspective-origin: 50% 50%;
    position: relative;
    animation: hueRotate 21s infinite linear;
}

.g-group {
    position: absolute;
    width: 1000px;
    height: 1000px;
    left: -500px;
    top: -500px;
    transform-style: preserve-3d;
    animation: move 12s infinite linear;
    animation-fill-mode: forwards;
}

.g-group:nth-child(2) {
    animation: move 12s infinite linear;
    animation-delay: -6s;
}

.item {
    position: absolute;
    width: 100%;
    height: 100%;
    background: url(./img/nebula.jpg);
    background-size: cover;
    opacity: 1;
    animation: fade 12s infinite linear;
    animation-delay: 0;
}

.g-group:nth-child(2) .item {
    animation-delay: -6s;
}

.item-right {
    /* background: red; */
    transform: rotateY(90deg) translateZ(500px);
}

.item-left {
    /* background: green; */
    transform: rotateY(-90deg) translateZ(500px);
}

.item-top {
    /* background: blue; */
    transform: rotateX(90deg) translateZ(500px);
}

.item-bottom {
    /* background: deeppink; */
    transform: rotateX(-90deg) translateZ(500px);
}

.item-middle {
    /* background: rgba(255, 255, 255, 0.5); */
    transform: rotateX(180deg) translateZ(1000px);
}

@keyframes move {
    0% {
        transform: translateZ(-500px) rotate(0deg);
    }

    100% {
        transform: translateZ(500px) rotate(0deg);
    }
}

@keyframes fade {
    0% {
        opacity: 0;
    }

    25%,
    60% {
        opacity: 1;
    }

    100% {
        opacity: 0;
    }
}

@keyframes hueRotate {
    0% {
        filter: hue-rotate(0);
    }

    100% {
        filter: hue-rotate(360deg);
    }
}